There is a need for uniformly spaced duplex DNA size standards (ladders) with different spacings in the range of 40 kilobase-pairs (kbp) to 10 megabase-pairs (Mbp) and above for use in pulsed field gel electrophoresis. Commercially available size markers (e.g. lambda-DNA ladders, yeast chromosomal markers) are inadequate. We propose to develop a complementary set of novel DNA ladders with spacings of 40 kbp to about 760 kbp and ranging from 40 kbp to about 10 Mbp (or higher) by using a patent-pending technology.